1. Field of the Invention
The present invention relates to an optical mouse and, more particularly, to an optical mouse and method for preventing abnormal operation of the same, capable of preventing the optical mouse from outputting a wrong movement value when the optical mouse passes through an interface of a surface having an obvious difference in brightness.
2. Description of the Related Art
In general, as shown in FIG. 1, an optical mouse is designed so that light 7 emitted from a light source 8 is reflected from a worktable surface 2, and the reflected light 6 is inputted through a lens 5 into an image sensor 3 consisting of a semiconductor chip. Therefore, the optical mouse 1 obtains a surface image by calculating a quantity of light incident into the image sensor 3.
Then, the optical mouse stores the currently obtained surface image as a sample frame, begins at the left-upper corner of the sample frame to perform zigzag scanning in unit of pixel, and finds a location of the sample frame having the highest correlation with a reference region of a reference frame to calculate moved direction and distance, V(X, Y).
Here, the optical mouse controls the quantity of light incident into the image sensor 3 to be maintained at a constant level in such a way that a shutter-on time of the image sensor 3 is decreased when a bright surface image is obtained in order to accurately read out the surface image, while the shutter-on time of the image sensor 3 is increased when a dark surface image is obtained.
However, it is not easy for the optical mouse to control the shutter-on time of the image sensor 3 in order to read out the image of the surface having an obvious difference in brightness.
FIG. 2 is a timing diagram of control signals which a conventional optical mouse generates in order to control an image sensor, and FIG. 3 shows images obtained by the control signals of FIG. 2.
While the optical mouse gradually moves on the surface, particularly, from a dark location past an interface having an obvious difference in brightness to a bright location, the optical mouse sequentially decreases shutter-on times T1, T2, T3 and T4 of the image sensor 3.
Thus, each of the shutter-on times T1, T2, T3 and T4 has a relative magnitude as follows:
T1>T2>T3>T4
The optical mouse generates shutter control signals Shutter_ctrl reflecting each reduced shutter-on time and sampling control signals Sampling_ctrl for obtaining surface images corresponding to shutter control signals, and transmits the generated control signals to the image sensor 3.
As a result, the image sensor 3 accumulates light which is inputted by shutter-on when the shutter control signals Shutter_ctrl received from the optical mouse become a high level. Then, the image sensor 3 responds to the sampling control signals Sampling_ctrl toggled to the high level, and obtains images corresponding to the quantity of light accumulated for the shutter-on time to provide the obtained images to the optical mouse.
In the case where the image sensor 3 obtains a first image 11 in response to the control signals Shutter_ctrl and Sampling_ctrl, because the shutter-on time T1 is adjusted to be suitable for the dark surface, the image sensor 3 is capable of obtaining the image accurately reflecting unevenness or dissimilarity of the dark surface.
Meanwhile, in case where the optical mouse gradually moves from the dark surface to the bright surface, the shutter-on times T2 and T3 are gradually reduced, so that the unevenness or dissimilarity of the dark surface becomes obscure step by step as in second and third images 12 and 13.
This phenomenon becomes stronger when the bright surface becomes more than a predetermined region as in fourth image 14.
On the way to do so, when the bright surface exceeds more than the predetermined region as in fourth image 14, no profile representing the unevenness or dissimilarity exists on the dark surface.
As mentioned above, when the conventional optical mouse passes through the interface of the surface having the obvious difference in brightness, it is impossible to properly adjust the shutter-on time for simultaneously sensing the two surfaces where the difference in brightness is obvious.
Consequently, the conventional optical mouse fails to discriminate the unevenness or dissimilarity of the surface. For this reason, there is a problem in that the optical mouse calculates a wrong movement value to cause abnormal operation.